This was revealed in an interview with Toyo Keizai (via Kotaku) where Capcom president Haruhiro Tsujimoto acknowledges the demand for the game. However he said, “We’re aware of that request. However, taking into account various conditions, bringing Monster Hunter: World now for release is difficult. The reason is that the Switch has different functions from other stationary consoles as well as different players.”
It is unclear as to what kind of difficulties he could be talking about, but presumably it could be due to the hardware of the Switch which might result in the game not being run optimally. Alternatively it could be certain mechanics of Monster Hunter: World that might not translate so well when brought onto the Switch.
However Tsujimoto points out that the company has already ported the 3DS Monster Hunter XX for the Switch. He also adds, “From now on, we’re looking at how we can support the Switch with our games, and that also includes Monster Hunter.”